The present invention relates generally to distance measurement systems and methods, and more particularly to systems and methods using multi-resolution functions to estimate distances precisely.
Distance measurement systems are widely used in technical and industrial fields. For example, the well known Global Positioning System (GPS) relies heavily upon precise distance measurements in order to provide accurate location information. Other systems, such as terrestrial and space-based telecommunication systems, military systems, and positioning systems for determining the location of natural resources represent a few which critically rely upon precise distance measurements.
Pen positioning systems are another example of systems which are heavily dependent upon precise position measurements. FIG. 1 illustrates one such exemplary system which may be used, for example, to provide a digitized version of one's handwriting. As known to those skilled in the art, the position of the pen in such systems must be precisely determined, typically be on the order of 0.5 millimeters (×10−3 m).
In its usual construction, the pen position system 100 includes a pen 102, sensors 104a and 104b and a processing unit 106. The position of the pen 100 on the paper 110 is determined using a triangulation process by which two distances d1 and d2 are determined from the pen 102 to two respective sensors 104a and 104b. In a particular embodiment of the system, pen 102 wirelessly transmits signals ST. The transmitted signals ST are received by sensors 104a and 104b, each received signal SR1 and SR2 having an associated phase shift corresponding to the distance d1 and d2 traversed from the pen's position 108. Concurrently, a reference signal Sref is communicated from the pen 102 to a processing unit 106, which also receives the phase shifted versions of SR1 and SR2 via sensors 104a and 104b. The processor 106 compares the reference signal Sref to the received phase-shifted signals SR1 and SR2, and therefrom obtains the relative phase differences of the received signals SR1 and SR2. The phase differences for each of the signals SR1 and SR2 can be easily translated to corresponding distances d1 and d2. Once d1 and d2 are determined, the pen's position 108 can be ascertained using conventional triangulation techniques.
The architecture of the conventional system is limited in the ability to provide high resolution and long distance measurements. If the transmitted signal ST is chosen at a relatively low frequency, the resolution may be insufficient to accurately locate the pen even though the system can measure longer distances. If a relatively high frequency is chosen, the phase of the higher frequency signal can provide higher resolution positioning information but can measure only short distances. The distance traveled by a cycle of the wave thus limits the system's ability to make global distance measurements which is a trade-off vis-à-vis the resolution of the measurements.
What is needed is a system and method for estimating distances in which a low resolution function is used for obtaining global measurements and a high resolution function is efficiently used for obtaining local measurements.